Speech transmission system



S D R A w D E G. P.

SPEECH 'TRANSMISSION SYSTEM Filed Feb. 27, 1941 /NVENTOR P G. EDWARDS V E N m n A Patented May 12, 1942 'UNITED STATES .PATENT GFEICE SrEEcn 'raANSMISsIoN SYSTEM Pani G. Edwards, verona. N. J., 'r to neu Telephone Laboratories,

Incorporated, New

York, N. Y., a. corporation of New York Application February 2'1,l 1941, Serial No. 380,909 4 claims. (ci. 179-170) ings 13 and 14.

It is common practice, of course, in the oper- A ation of a speech transmissionsystem of the type which includes a telephone repeater in the line to transmit, in addition to the voice frequency telephone currents, other currents.- For example, direct current may be transmitted for dialing purposes, for energization of supervisory signals at the central omce or for energiz'ation of the subscribers telephone transmitter.` Low frequency alternating current (usually of the order of 20-) may also be transmitted for Signaling purposes. In the past transmission of these auxiliary currents has presented perplexing and expensive problems. The telephone repeater, being designed to amplify currents of the order of voice-frequency, is not adapted to pass thev di-` rect current or the low frequency alternating current without resultant distortion so that it has been necessary heretofore to provide means for by-passing these currents around the repeater. The by-pass arrangements of prior systems' have, in general, been expensive, have oiered complex balancing problems and have resulted in substantial transmission loss.-

A feature of the present invention is a continuous straight-throughmpath of direct current and low frequency alternating current from one of the line sections to the other line section.

A complete understanding of the novel arrangements contemplated by the present invention as well as appreciation of the desirable features thereof will be gained by consideration of the following detailed description in connection with the annexed drawing, the single figure of which illustrates a telephone repeater including a novel path fordirect current and low frequency alternating current of the nature contemplated by the present invention.

Referring now to the drawing, two speech transmission line sections Lw and Le are shown coupled by respective hydrid coil sets Il and I2 to west-east amplier I3 and east-west amplifier I4. Hybrid coil set II includes two separate cores I5 and I6, core I5 being provided with line windings I1 and 2I, amplifier windings 22 and 23 and balancing network windings 24 and 25, while core I6 is provided with line windings 26 and 21, amplier windings 4I` and 42 and balancing network windings 43 and 46.

' Hybrid coil set I2 includes two cores 45 and 46. core 46 being provided with line windings 41 and 6I, amplier windings 62 and 58 and balancing network windings 64 and 66, while core 46 is provided with line windings 56 and 61,' amplifier windings 1I and 82 and balancing network wind- Hybrid coil setI II and associated balancing network or articial line- 16 act to couple input path 16 of west-east amplifier I3 and output path 11 cineast-west amplifier I4inconjugate relationship with each other and in energy transmitting relationship with line section Lw; similarly, hybrid coil set I2 and associated balancing network or artificial line 8I act to couple output path 82 of amplier I3 and input path 83 of amplifier I4 in conjugate relationship with each other and in energy transmitting relation- -ship with line Section Le.

Voice frequency currents received over line section Lw from the west terminal divide, onehalf' passing into output path 11 of east-west 'amplifier I4 and being lost and the usefulhalf passing into input path 16 of west-east amplifier I3. These currents, after ampliilcation by amplifier I3, are impressed on line section Le. As output path 82 and input path 83 are coupled in conjugate relationship, as'pointed out above, no part of these amplified currents enters the input path of amplifier I4.

In a manner similar tothat just described, voice frequency currents received over line section La from the east terminal divide one-half being lost in output path 82 and the useful halfv being ampliiied by east-west amplifier I4 and impressedon line section Lw.

As pointed out above, direct current and low frequency alternating current need be transmitted over the lin'e for dialing, supervision, battery supply andthe like. As illustrated, a direct continuous path is provided for these currents, one side of the path including as series elements line windings I1 and 26 of hybrid coil set II, inductances 84 and 85 and line windings 41 and 56 of hybrid coil set I2 and the other side of the path including as series-elements line windings 2I and 21 of hybrid coil set II, inductances 86 and 81 and line windings 5I and 51 of hybrid coil set I2. Inductances 84, 85, 86 and 81 and capacitances IIlI and |02 provide filtering action eiective to exclude the voice frequency currents from this path.

The provision of the straight-through continuous path contemplated by the present invention results in low loss transmission of the direct currents and low frequency alternating currents directly through the repeater section ineither f pensive elements and the perplexing problem of preventing unbalance of the speech transmission circuits attendant upon provision of the by-pass paths of prior arrangements are entirely eliminated and a substantial transmission gain, as compared to the performance of prior arrangements, is achieved.

.While a specific embodiment of the invention has been selected for detailed description, the invention is not limited in its application to the .l-

embodiment described. This embodiment should be taken as illustrative of theinvention and not as restrictivethereof.

What is claimed is:

1. In combination with a two-way line divided into sections, a two-way repeater comprising two one-way amplifying paths for repeating in respectively opposite direction between opposite sections of line, a separate differential transformer included between each line section and said two paths, each such transformer comprising a pair of magnetic cores, line windings connected to the respective line sections and mounted in each case on both cores of the respective transformer, a balancing artificial line for each line section, windings mounted on both cores of the respective transformer and connected to the respective artificial line, other windings mounted on certain of said cores in the case of each transformer and connected respectively in circuit with the input side of one of said one-way paths and the output side of the other ofsaid one-way paths, and a path for through transmission of currents of low frequencies including direct current extending from one line section to the other through said line windings of both transformers in series, said path consisting, between the respective points of connection to said line windings, of two lines and means for excluding therefrom voice frequency currents.

2. In combination with a two-way line divided into sections, a two-way repeater comprising two one-way amplifying paths for repeating in respectively opposite direction between opposite sections of line, a separate differential transformer included between each line section and said two paths, each such transformer comprising a pair of magnetic cores, line windings connected to the respective line sections and mounted in each case on both cores of the respective transformer, a balancing artificial line for each line section, windings mounted on both cores of the respective transformer and connected to the respective artificial line, other windings for each of said transformers connected respectively in circuit with the input side of one of said one-way paths and the output side of the other of said one-way paths,

said other windings in the case of each transformer being mounted on a different one of said cores, and a path for through transmission of currents of low frequencies including direct current extending from one line section to the other through said line windings of both transformers in series, said path consisting, between the respective points of connection to said line windings, of two lines and means for excluding therefrom voice frequency currents.

3. In a speech transmission system, a west amplii'ler for voice frequency currents, an east lampliiier for voice frequency currents, a two-wire west line section, a two-wire east line section, a first hybrid coil set andja rst balancing network for coupling said west line to the input of said west amplifier in speech energy transferring relationship, for coupling the output of said east amplifier and said west line section in speech energy transferring relationship and for coupling the output of said east amplifier to the input of said west amplier in conjugate relationship, said first hybrid coil set comprising a first core and a second core, a first line winding and a second' line winding on said first core, a first line winding and a second line winding on said second core, said first line windings being connected ln series with each other and with one side of said west line section, said second line windings being connected in series with each other and with the other side of said west line section, a second hybrid coil set and a second balancing network for coupling said east line section to the input of said east amplifier in speech energy transferring relationship, for coupling the output of said west' amplifier to said east line section in speech energy transferring relationship and for coupling the output of said west amplifier to the input of said east amplifier in conjugate relationship, said second hybrid coil set comprising a first core and a second core, a first line winding and a second line winding on said first core of said second hybrid coil set, a rst line winding and a second line winding on said second core of said second hybrid coil set, said last-mentioned rst line windings being connected in series with each other and with one side of said east line section, said last-mentioned second line windings being connected in series with each other and with the other side of said east line section, and a direct current transmitting path connected directly in series with said line windings of said two hybrid coil sets, said direct current path consisting, between the respective points of connection to said line windings, of two lines and means for excluding therefrom voice frequency currents.

4. In combination with a two-way line divided into sections, a two-way repeater comprising two one-way amplifying paths for repeating in respectively opposite direction between opposite sections of line, a separate differential transformer included between each line section and said two paths, each such transformer comprising a pair of magnetic cores, line windings connected to the respective line sections and mounted in each case on both cores of the respective transformer, a balancing artificial line for each .line section, windings mounted on both cores of the respective transformer and connected to the respective articial line, other windings for each of said transformers connected respectively in circuit with the input side of one of said oneway paths and the output side of the other of said one-way paths, said other windings in the case of each transformer being mounted on a different one of said cores, the input side of each one-way path being conjugate to the output side of the opposite one-way path and a path for through transmission of currents of low frequencies including direct current extending from one line section to the other through said line windings of both transformers in series, said path consisting only of two lines, inductance elements in series with each line and capacitance elements in shunt to the two lines.

PAUL G. EDWARDS. 

